Cannons are typically efficient in accelerating a projectile. However, the velocity of the projectile in the barrel of the cannon is limited. At high velocities in a cannon, the pressure on the base of the projectile drops rapidly as the projectile velocity exceeds the speed of sound in the gun gasses. The drop in the pressure at the base limits the projectile speed to a few times the speed of sound in the medium. A so-called “traveling charge” extends the velocity limit For example, to further accelerate the projectile, a traveling charge is ignited after both the charge and the projectile initially accelerate forward.